Methods and systems for current sharing between power semiconductors in an assembly are provided. The power semiconductor assembly includes a plurality of power semiconductors, each comprising at least one output conductor, the plurality of output conductors are electrically coupled together in parallel, an output bus network configured to transpose the output conductors such that magnetic fields causing a current output imbalance between the plurality of power semiconductors are substantially canceled.
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1. A power semiconductor assembly comprising:
a plurality of power semiconductors, each comprising at least one output conductor, said plurality of output conductors are electrically coupled together in parallel; and
an output bus network configured to transpose said output conductors such that magnetic fields causing a current output imbalance between said plurality of power semiconductors are substantially canceled.
13. A power converter comprising:
a power semiconductor assembly comprising a plurality of power semiconductors having respective output conductors electrically coupled in parallel, said conductors transposed about at least one axis such that magnetic fields causing a current output imbalance between said plurality of power semiconductor substantially cancel each other; and
a control unit for controlling said power semiconductor assembly to generate an electrical output.
25. A method of balancing output current in a semiconductor assembly that includes a plurality of power semiconductors wherein each power semiconductor includes at least one output current-carrying conductor, said method comprising:
determining a relative orientation of te power semiconductors in the semiconductor assembly; and
transposing the output conductors about at least one axis of symmetry defined by the relative orientation of the plurality of power semiconductors.
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This invention relates generally to power semiconductors, and more particularly to methods and systems for current sharing between parallel connected power semiconductors.
At least some known power converters utilize power semiconductor switches. The power semiconductor switches' current outputs may be coupled in parallel when a desired output current is greater than the current capability of one power semiconductor switch by itself. Imbalance in current sharing between semiconductor switches coupled in parallel limit an amount of total output current that may be produced by the power converter. More specifically, in such instances, the highest stressed power semiconductor switch limits the power converter output, such that the lower stressed power semiconductor switches do not achieve their full capability.
Generally, an output current of power semiconductor switches is at least partially dependent on the electrical characteristics of each power semiconductor switch. Another factor which may affect the output of power semiconductor switches is magnetic interaction between the magnetic fields generated by each output current, and/or magnetic fields generated by other current carrying conductors or other sources, for example, one or more current return paths. In limited applications, power semiconductor switches may be positioned to facilitate minimizing such effects. However, multiple magnetic field sources and/or unknown magnetic field sources may make balancing output currents between power semiconductor switches difficult to achieve.
In one aspect, a power semiconductor assembly is provided. The power semiconductor assembly includes a plurality of power semiconductors, each comprising at least one output conductor wherein the plurality of output conductors are electrically coupled together in parallel, an output bus network configured to transpose the output conductors such that magnetic fields causing a current output imbalance between the plurality of power semiconductors are substantially canceled.
In another aspect, a power converter is provided. The power converter includes a power semiconductor assembly comprising a plurality of power semiconductors having respective output conductors electrically coupled in parallel, the conductors are transposed about at least one axis such that magnetic fields causing a current output imbalance between the plurality of power semiconductor are substantially canceled, and a control unit for controlling the power semiconductor assembly to generate an electrical output.
In yet another aspect, a method of balancing output current in a power semiconductor assembly is provided. The power semiconductor assembly includes a plurality of power semiconductors wherein each power semiconductor includes at least one output current-carrying conductor. The method includes determining a relative orientation of the power semiconductors in the semiconductor assembly, and transposing the output conductors about at least one axis of symmetry defined by the relative orientation of the plurality of power semiconductors.
Output bus network 104 includes at least one output conductor 108 for each respective power semiconductor 102 that is electrically coupled in parallel. Current flowing in output conductor 108 generates a magnetic field 110 that radiates circumferentially from output conductor 108. Magnetic lines of flux 112 may interact with other magnetic lines of flux 112 radiating from other conductors 108. Such interaction may cause current in the respective generating conductors to vary in accordance with the interaction between the magnetic lines of flux 112. Output bus network 104 is configured such that output conductors 108 are transposed about an axis of symmetry 109. Accordingly, magnetic fields 110, which may cause an output current imbalance between the plurality of power semiconductors 102 substantially cancel each other.
A relative location of current return path 106 with respect to power semiconductors 102 may determine a configuration of output bus network 104 that facilitates canceling the magnetic fields that may cause an imbalance of output current from power semiconductors 102. Moreover, the location of current return path 106 causes the current sharing to be imbalanced, due to the magnetic flux path effectively pulling the output current toward current return path 106. As such, the current in output conductors 108 that lie closest to current return path 106 have relatively more current flow than output conductors 108 farther from current return path 106. In the exemplary embodiment, the relative location of current return path 106 is such that transposition in only one axis 109 is needed. It should be understood that magnetic fields from other sources may also interact with the magnetic fields generated by output conductors 108 to cause an imbalance of output currents between power semiconductors 102.
In the exemplary embodiment, current return path 206 is substantially aligned with axis 210. When current return path 206 is substantially aligned with axes 109 or 210, transposition in only one axis is needed. Accordingly, output conductors 208 associated with power semiconductors 201 and 203 are transposed and output conductors 208 associated with power semiconductors 202 and 204 are transposed. Output conductors 208 are coupled together downstream of the transposition to form a combined output 211. Combined outputs 211 may be coupled together to form a power semiconductor assembly output 212.
In an alternative embodiment, current return path 206 is substantially aligned with respect to an axis 214 wherein output conductors associated with power semiconductors 201 and 202 are transposed and output conductors associated with power semiconductors 203 and 204 are transposed. Accordingly, the axis about which the transposition of output conductor 208 is made is substantially determined by the location of return path 206 with respect to power semiconductors 201, 202, 203, and 204, and the configuration of power semiconductors 201, 202, 203, and 204.
In the exemplary embodiment, four power semiconductors 401, 402, 403, and 404 are positioned in a two-by-two configuration and electrically coupled in parallel. Alternatively, power semiconductors 401 and 403 are positioned substantially symmetrically about a vertical axis 410 with respect to power semiconductors 402 and 404, and power semiconductors 401, 402 are positioned substantially symmetrically about a horizontal axis 412 and with respect to power semiconductors 403 and 404. A first contact 414 of output conductor 408 is coupled to a termination point 416 of power semiconductor 401. Output conductor 408 extends to a bend 418 that directs output conductor 408 diagonally toward a bend 420 that directs output conductor 408 away from power semiconductor 404 and substantially coincident with a line 424 extending normally from a midpoint 422 of power semiconductor 404. Output conductor 408 also extends along line 424 to a bend 426 that directs output conductor 408 back towards power semiconductor 401 and to a bend 428 positioned approximately normal to an intersection of axes 410 and 412. Output conductors associated with power semiconductors 402, 403, and 404 are not shown but, should be understood to follow complementary paths similar to the path of output conductor 408. The two-axis transposition of all four conductors of output bus network 405 facilitates canceling current imbalance in power semiconductors 401, 402, 403, and 404 from multiple current return paths 406 and/or a current return path 406 that is not directly aligned a vertical axis of symmetry and/or a horizontal axis of symmetry.
Similarly to the transposition described with reference to
The above-described methods and systems for current sharing between parallel connected power semiconductors is cost-effective and highly reliable for facilitating improving the output of power semiconductor assemblies. More specifically, the methods and systems described herein facilitate improving the current output of a plurality of parallel connected power semiconductors such that externally induced magnetic fields cause substantially equal effects in each current output conductor and current flow output between each power semiconductor is substantially equalized. As a result, the methods and systems described herein facilitate power semiconductor assembly output in a cost-effective and reliable manner.
Exemplary embodiments of power semiconductor assemblies and methods are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each system component can also be used in combination with other system components. In the exemplary embodiments described herein, a current return path of the power semiconductors is illustrated as being a the source of-the magnetic field that cause the current imbalance in the power semiconductor current outputs. It should be understood that magnetic fields from other sources may also interact with the magnetic fields generated by output conductors to cause an imbalance of output currents between power semiconductors.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
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